This invention relates to light sources for use underwater, and, more particularly, to a compact high intensity light source particularly useful in the motion picture industry.
When motion pictures are filmed, the director often calls for artificial lighting in scenes, beyond that available from ambient natural lighting. The artificial light may be utilized to increase the general level of illumination so that slower speed film can be used, to highlight particular features, to illuminate otherwise darkened areas, or for other purposes. Important requirements of such lighting are that it be of sufficient intensity, that it be of the form needed, such as a narrow spot or broad flood of light, that it be conveniently provided, and that it be of a natural coloration so that the colors of the scene are not distorted.
Underwater movies have grown in popularity in recent years, and scenes filmed underwater pose some particular problems for cameramen and lighting engineers. The available ambient light level decreases with increasing depth and there is often little illumination of features on the bottoms of objects, so that artificial lighting is utilized in nearly all scenes.
Underwater lighting sources have the same requirements of intensity, form, convenience and coloration as lighting sources used out of water, but the ability to meet these requirements is made difficult by some of the technical limitations of the light sources. One approach to underwater lighting has been to plunge conventional lamps available in the industry, but connected to their power sources by rubber potted cables, directly into the water. This approach continues to be used, but is not fully satisfactory for several reasons. The halogen cycle lamps often used are cooled too strongly, and may never be able to reach their proper operating temperature of 485.degree. F. The result is color deviation in the film and reduced operating life of the lamp. Because the water attenuates the light from the lamp, a generally higher intensity, more powerful lamp is required underwater than for an otherwise equivalent above-water scene. The lamps often burn out after short times or a few on-off cycles, primarily due to the boiling of water in contact with the glass envelope of the lamp that tends to crack the glass. Powerful lamps are large in size and unwieldy. They are heavy and difficult to place and move, a major inconvenience because such work must be done by divers. The glass envelopes of incandescent lamps are not made to resist the high pressures found at depths greater than about 150 feet.
In another approach, small or medium size incandescent or halogen cycle lamps have been placed into watertight housings and operated underwater. In most cases, the lamps are not sufficiently powerful for use in underwater filming, or, if sufficiently powerful, are extremely large in size.
Accordingly, there is a need for an improved underwater lighting source for the motion picture industry. The present invention fulfills this need, and further provides related advantages.